Gas turbine engines may be used to power various types of vehicles and systems. A typical gas turbine engine includes at least a compressor, a combustor, and a turbine, and may include additional components and systems, depending on the particular end-use of the gas turbine engine. During operation of a gas turbine engine, the compressor draws in, and raises the pressure of, ambient air to a relatively high level. The compressed air from the compressor is then directed into the combustor, where a ring of fuel nozzles injects a steady stream of fuel. The injected fuel is ignited, which significantly increases the energy of the compressed air. The high-energy compressed air from the combustor then flows into and through the turbine, causing rotationally mounted turbine blades to rotate.
A gas turbine engine may be used to supply propulsion power, electrical power, and/or pneumatic power. For example, many aircraft use gas turbine engines as auxiliary power units to supply pneumatic power for various systems and functions. These systems and functions may vary, and may include the aircraft environmental control system, the cabin pressure control system, and/or main engine start (MES) air. The pneumatic power is, in many instances, provided by bleeding compressed air from a centrifugal load compressor that is driven by the turbine.
More specifically, during gas turbine engine operation, the load compressor draws in ambient air, via an air inlet, and compresses the air. A plurality of inlet guide vanes are mounted adjacent the inlet and are movable via one or more actuators. By selectively adjusting the position of the inlet guide vanes the flow rate of air entering the load compressor, and thus the flow rate of bleed air supplied to the various systems and functions, may be regulated.
The above-described gas turbines may, under certain operating scenarios, experience maximum operating conditions due to a limit of available fuel flow rate. This can occur, for example, if the mechanical load on the turbine is too high while the fuel flow rate to the gas turbine engine is at a maximum. When a limited fuel delivery condition occurs, the turbine speed will begin to drop below the commanded speed. If the turbine speed drops too low, then gas turbine operation may be compromised.
Hence there is a need for a system and method that will reduce the mechanical load on the turbine relatively quickly when a limited fuel delivery condition occurs so that the speed of the turbine may quickly recover. The present invention addresses at least this need.